Interface Effects on Total Energy Calculations for Radiation-Induced Defects

We present a new, approximate technique for estimating the polarization energy of point defects near interfaces in layered systems using semiconductor device simulation combined with a finite element quadrature technique. We show that we recapture the original, spherical Jost approximation in a homogeneous, infinite solid, as well as reproducing the exact result for a point charge near the interface of two dielectrics. We apply this technique to the silicon-silicon dioxide system for doped substrates, and for devices under bias. We show that the correction to calculated, bulk defect levels depends mildly on the distance from the interface. It depends more strongly on the substrate doping density. Finally, there is a significant dependence on gate bias. These results must be considered for proposed models for negative bias temperature instability (NBTI) that invoke tunneling from the silicon band edges into localized oxide traps.